Aspects of the present disclosure relate generally to wireless communication systems, and more particularly, to power control for multicarrier uplink transmission.
Wireless communication networks are widely deployed to provide various communication services such as telephony, video, data, messaging, broadcasts, and so on. Such networks, which are usually multiple access networks, support communications for multiple users by sharing the available network resources. One example of such a network is the Universal Mobile Telecommunications System (UMTS) Terrestrial Radio Access Network (UTRAN). UTRAN is a radio access network (RAN) defined as a part of UMTS, a third generation (3G) mobile phone technology supported by the 3rd Generation Partnership Project (3GPP). UMTS, which is the successor to Global System for Mobile Communications (GSM) technologies, currently supports various air interface standards, such as Wideband-Code Division Multiple Access (W-CDMA), Time Division-Code Division Multiple Access (TD-CDMA), and Time Division-Synchronous Code Division Multiple Access (TD-SCDMA). UMTS also supports enhanced 3G data communications protocols, such as High Speed Packet Access (HSPA) and High Speed Uplink Packet Access (HSUPA), which provide higher data transfer speeds and capacity to associated UMTS networks.
In HSUPA systems, a user equipment (UE) may transmit uplink physical channels over multiple carriers that may include a dedicated physical control channel (DPCCH) or enhanced DPCCH (E-DPCCH). When the UE has more than one activated uplink carrier, also referred to as an activated uplink frequency, the UE estimates the remaining power that is available to be allocated to scheduled enhanced dedicated channel (E-DCH) transmissions by taking into account the DPCCH/E-DPCCH for each carrier. In particular, the UE may perform an E-DCH transport format combination (E-TFC) selection procedure that is first applied to a Secondary Uplink Frequency and then to a Primary Uplink Frequency. In observing different field scenarios, however, it has been noticed that different schedulers and different power management techniques at the network level affect the effective UE performance. For instance, if there is any imbalance between the multiple uplink carriers, effective data transmission as well as reliability of the data transmission might be degraded. For example, a UE may have a significant power imbalance (perhaps more than 5 dB) between the first carrier C0 (e.g., Primary Uplink Frequency) and the second carrier C1 (e.g., Secondary Uplink Frequency), due to strong interference on C1 such that it takes significantly more power (perhaps more than twice the power) to send data on carrier C1 than on carrier C0. As an example and as illustrated in FIG. 2A (which is described later in detail), a UE may have an allowed maximum power of 24 dBm 212, based on an uplink data grant 214 of 1000 bits on carrier C0 and 5000 bits on carrier C1. Power splitting for the carriers C0 and C1 may be proportionally allocated based on the data grant, where power P0 to carrier C0 is (1000/6000)24=4 dBm, and power P1 to carrier C1 is (5000/6000)24=20 dBm. However, due to the significant power imbalance and poor reliability of carrier C1, an E-TFCI assignment to the UE (e.g., the predefined maximum allowable throughput based on reliability of the channel) for the data transmission on carrier C1 is severely limited to only 1500 bits of the allocated 5000 bits. Otherwise, if carrier C1 was not impeded by interference, the E-TFCI selection could allot significantly more data bits. Meanwhile, the stronger carrier C0 may be limited to sending only 500 bits of the allocated 1000 bits based on E-TFCI for 4 dBm, which was due to the low power split based on the proportional grant. As such, current techniques may not maximize an amount of data that can be transmitted.
An additional issue with current 3GPP specifications relating to dual carrier HSUPA (DC-HSUPA) operation is that data to be transmitted is first sent on the second carrier (e.g., the Secondary Uplink Frequency) and then on the first carrier (e.g., the Primary Uplink Frequency). Accordingly, high priority data, which is selected to be sent first, is to be transmitted on the second carrier. In a case where an inferior carrier C1 is the second carrier, however, this high priority data is at risk of transmission failure due to the currently specified procedures.
Thus, improvements in transmitting uplink physical channels over multiple carriers are desired.